Virtual volume flow sensor
In the context of Industry 4.0 and condition monitoring, precise and inexpensive measurement principles and sensors are becoming increasingly important. Volume flow sensors are hardly ever installed, as they only provide accurate measured values for the stationary and laminar case. Furthermore, volume flow sensors are installed invasively, which means that the sensor itself causes a pressure change and a more complex system structure. This in turn means that the most important variable of the fluid power system, the performance, cannot be monitored. The aim of this research project is therefore to implement a non-invasive measurement principle that enables the simultaneous recording of volume flow and pressure and thus of the power flow within a fluid power system.
| Benefit | Procedure |
|---|---|
| No invasive installation of a volume flow sensor | Derivation of the transient equations for the laminar and turbulent case |
| Accurate measurement accuracies that go beyond the stationary, laminar case | Validation through simulations |
| Effective use of the recorded data | Development of a test rig and validation in practice |
| No more need for a volume flow sensor |
Challenges of volume flow measurement in fluid power
Today's volume flow sensors are not capable of detecting highly unsteady flows. This is either because the response of the sensors is too sluggish or the measurement method is only valid for steady flows. The measuring principle behind the volume flow sensors is based on Hagen-Poiseuille's law, which can calculate the volume flow in a pipe for stationary and laminar flows with the help of pressure measurements. However, stationary and laminar flows are rarely present in technical systems. Therefore, it is not possible to calculate the volume flow based on pressure measurements and current concepts based on this cannot work in the general case.
Benefits of a volume flow soft sensor
The extension of the measuring range for turbulent and unsteady flows supports in particular the domain of condition monitoring of fluid power systems. Especially in small to medium-sized hydraulic systems, as found in small stationary plants or in mobile hydraulics, only pressure and temperature sensors are often used for cost reasons. By using a virtual image of a volume flow sensor, even such systems can measure volume flows and power. Due to the uniform system monitoring, a system failure can be predicted. Such a failure leads to considerable costs in stationary hydraulics, since the machine has to be replaced and the downtime means enormous production delays. Furthermore, by measuring volume and power flow, increased internal leakage caused by wear can be detected. Internal leakage results in increased dissipated power, which in turn leads to increased operating costs.
Volume flow measurement via soft sensor
The VirtVolSensor research project focuses on closing the research gap, i.e. the generalization of the Hagen-Poiseuille equation for the transient case. This is achieved by establishing a design methodology for the use of a virtual volume flow sensor based on pressure measurements.
Derivation of an analytical model for the transient case
First, the theoretical basis for the calculation of transient laminar as well as turbulent flows for volume flow measurement based on pressure measurements has to be worked out. This includes the derivation of a set of equations for the transfer behavior in the time domain.
Validation using a simulation model and a test rig
The mathematical model obtained is then validated. For this purpose, a simulation model and a test bench are created. The simulation model is used for the validation of the general case and a test bench validation is performed for selected cases.
Acknowledgement
The IGF research project 21475 N / 1 of the research association Forschungskuratorium Maschinenbau e. V. – FKM, Lyoner Straße 18, 60528 Frankfurt am Main was supported from the budget of the Federal Ministry of Economic Affairs through the AiF within the scope of a program to support industrial community research and development (IGF) based on a decision of the German Bundestag.